1. Field of the Invention
This invention generally relates to medical diagnostic imaging systems, and in particular, relates to methods and systems for improving three-dimensional volume reconstructions from two-dimensional x-ray images in navigationally guided operations making use of an X-ray diagnostic machine.
2. Description of the Related Art
Medical operations on living subjects are increasingly being done with navigational support systems. Such systems typically involve the guiding of an instrument by means of a position detection system relative to a tissue region of the subject undergoing treatment. Of special interest is navigation in regions not amenable to the visual inspection of the surgeon, because, for example, the instrument has been introduced inside of the subject. Under these circumstances, the instrument, such as a catheter, is guided in a virtual 3D volume, which has been generated by means of a projection method before or during the operation. A frequent application is to use an X-ray diagnostic machine to generate a series of 2D projection images of a known projection geometry and then to generate a 3D volume data set from these 2D images. The volume data set is relayed to a navigation system, which has a position detection system for marks which can be detected in this way.
In order to make possible high-precision navigation, the system of coordinates of the position detection system can be adjusted to the coordinate system of the 3D volume data set. This process is usually known as registration. During registration, for example, one often uses a phantom which contains X-ray positive marks and marks detectable by a position detection system in a fixed spatial relation to each other. To improve the precision of a reconstructed 3D data set from 2D X-ray projection images, there are known methods which allow for the deviations of the parameters of the projection geometry from the actual projection geometry, influenced, for example, by mechanical torsions of the X-ray diagnostic machine. For this, an X-ray diagnostic machine is “calibrated” by using a special X-ray phantom. Such a calibration is generally done only before being shipped from the factory, after a repair with replacement of mechanical components, or before the start of an investigation.
German patent DE 102 02 091 A1 discloses a device and method for determining a coordinate transformation by using a phantom, on which X-ray positive marks and marks detectable by a position detection system are arranged in a fixed spatial relation to each other. During a scan to create 2D X-ray projection images, the coordinates of the X-ray positive marks are determined in the reconstructed 3D volume and relayed to the position detection and navigation system for adjustment.
U.S. Pat. No. 5,442,674 A and German Patent 199 47 382 C2 disclose known X-ray phantoms by means of which the mechanical insufficiencies of the X-ray diagnostic machine are corrected in a calibration process outside of a surgical use.
U.S. Pat. No. 5,835,563 A concerns an X-ray phantom that remains firmly connected to the patient during an X-ray exam and improves the accuracy of the representations during digital subtraction angiography (DAS).
Certain embodiments of the present invention are adapted to improve the intraoperative volume reconstruction during navigationally guided operations by using an X-ray diagnostic machine and a position detection system in a simple and cost-effective manner.